Compression seal canister
The present invention relates to canisters and more particularly to canisters such as those used in gas masks for protection against toxic agents. 
     The known canisters are satisfactory in many respects, but are subject to certain manufacturing limitations. In the manufacture of the existing canisters an adsorbent material, normally charcoal, is deposited in a level bed in the bottom of a canister. Pressure is applied to the charcoal bed and a diaphragm is locked in place under pressure by rolling a groove in the canister body to keep pressure on the bed. A preformed filter for particulate materials and a top diaphragm are then placed over the charcoal bed, with an adhesive sealant around the outer edge. After four hours of exposure the adhesive is sufficiently cured that a cover may be mounted on the canister. The canister may then be sealed with a rubber plug pushed into the inlet opening in the cover and a screw cover fitted to the bottom outlet opening. 
     With this procedure, the charcoal is left exposed to ambient conditions in the assembly area for a considerable time (4 hours or more). The adhesive used currently is a room temperature vulcanizing silicone sealer that requires moisture in the ambient atmosphere in order to cure. This may lead to an excessive moisture content in the hydroscopic carbon. The assembly plant can be air conditioned to provide a very dry atmosphere, but this is contrary to the requirements for curing the sealer, is expensive and causes discomfort to workers in the area. 
     Furthermore, the full curing time of the sealant is up to 16 hours, so that the sealant continues to cure inside the closed container. A by-product of this curing is acetic acid, which accumulates in the canister and makes the initial use of the canister very unpleasant. 
     The present invention is concerned with a solution to this problem. 
     According to one aspect of the present invention there is provided a particulate filter for use in a gas mask filter canister comprising a filter element and a sealing ring extending peripherally around the filter element, the sealing ring having a tapered outer face for a force fit engagement with an inner face of the filter canister housing. 
     The compression seal produced by the ring eliminates the four hour adhesive curing time during which the charcoal adsorbent is exposed to the ambient assembly area atmosphere. The new canister and filter also lend themselves more fully to an automated assembly process than does the prior art canister. 
    
    
     In the accompanying drawings, which illustrate exemplary embodiments of the present invention: 
     FIG. 1 is a cross section of a prior art canister; 
     FIG. 2 is a similar cross section of a canister according to the present invention; 
     FIG. 3 is a cross section of a filter for use in a canister according to the presentation invention; and 
     FIG. 4 is a detail view showing the interaction of the canister housing, the sealing ring and the retainer. 
    
    
     Referring to the drawings, and particularly to FIG. 1, there is illustrated a prior art canister 10. This canister has a canister body consisting of a housing 14 and a cover 16. The housing 14 accommodates a bed of activated charcoal 18 sandwiched between layers of an appropriate retaining medium 20 that serves to confine the charcoal to its bed while permitting the passage of gas through it. 
     Annularly corrugated retainers 22 and 23 are mounted on opposite sides of the charcoal bed. Retainer 22 is assembled with pressure on the bed of charcoal 18 then locked in place with a grooving wheel acting on the exterior wall of the canister. Deflection of the retainer 23 is resisted by an annular support sleeve 28 that extends from the bottom of the retainer 23 to a flange 29 on a threaded mounting coupling 30 of the canister housing 14. 
     Mounted in the canister above the charcoal bed is a pleated paper filter 32 surrounded by a polyurethane gasket 34. The gasket 34 is sealed to the inside wall of the container housing 14 by an adhesive seal 35. An annularly corrugated diaphragm 36 is mounted on the top of the filter 32. The canister housing is closed by a cover 38 joined to the side wall of the housing 14 by a double rolled seam 40. This is a standard seam used in canning. The center of the cover has a circular opening 46 to provide for the passage of air to be purified into the canister. 
     The canister illustrated in FIG. 1 is subject to certain disadvantages. Because the charcoal bed 18 is installed in the housing 14 as one of the first steps in assembly, and because it takes roughly sixteen hours to cure the adhesive joining the polyurethane gasket 34 of the pleated paper filter 32 to the housing 14, the charcoal is exposed to the ambient atmosphere in the assembly area for a lengthy time, at least sufficient time for the adhesive to develop a skin. 
     A new canister design that addresses this problem is illustrated in FIG. 2. The canister 50 has a canister body 52 consisting of a housing 54 and a cover 56. The housing accommodates a bed of activated charcoal 58 sandwiched between layers of an appropriate retaining means 60 that confines the charcoal to the bed while permitting the passage of gas through it. Two annularly corrugated retainers 62 and 63 are fitted on opposite sides of the charcoal bed. Deflection of the lower retainer 63 is resisted by an annular support sleeve 64 that extends from the bottom of the retainer to a flange 66 on a threaded coupling 30 of the canister. 
     Mounted in the canister above the charcoal bed is a particulate filter 70. This is a pleated paper filter medium 72 surrounded by a sealing ring 74 of resilient polyurethane material. The sealing ring is molded onto the outer periphery of the paper filter. The lower end of the sealing ring extends over the inside face of a flange 76 at the periphery of the retainer 62. The flange extends along the inside face of the housing. At the top of the filter 70, above the paper component 72 is a retainer 78 with a peripheral flange 80 that engages the sealing ring 74 above the paper and compresses it against the inside wall of the housing 54. The cover 56 is secured to the side wall of the housing 54 with a seam 84 and compresses the sealing ring 74 vertically. 
     The relaxed configuration of the sealing ring 74 is illustrated most particularly in FIG. 3. As will be observed from that Figure, the sealing ring extends above and below the paper filter component 72. It has an inner cylindrical face 86 and an outer face 88 that tapers from the top to the bottom. The outer face 88 has a lower section 90 with a taper angle A of about 3° and an upper section 92 with a taper angle B of about 15°. Between the bottom face and the inner face 86 there is a bevelled surface 94. 
     When the filter is installed in the canister body, the sealing ring 74 is deformed as illustrated in FIG. 4. The inner face of the housing 54 is cylindrical and of smaller diameter than at least the upper section 92 of the sealing ring. Thus, the lower end of the sealing ring may be inserted into the housing, on the inside of retainer flange 76, to engage the retainer and form a seal at 96 along the bottom edge of the sealing ring 74. Towards the top of the retainer flange 76, the outer face of the sealing ring engages the inner face of the flange 76 to provide a second annular seal 98. Near the top, where the upper section 92 of the outer face is compressed against the inside face of the housing 54, there is yet another seal area 100. In this case, the deformation of the sealing ring is resisted by the peripheral flange 80 on the retainer 78 so as to provide a very strong engagement between the sealing ring and the side wall of the housing. When the cover 56 is installed and the chime completed, the cover presses down on the top face of the sealing ring 74 to provide a further seal 102. 
     A compression seal produced in this way can be made very quickly, without the need for additional adhesives and the consequent exposure of the charcoal to moist ambient conditions for a lengthy time, and without the generation of undesirable vapors in the sealed unit. 
     While one embodiment of the invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. Thus, while the unit described in the foregoing has been described as circular or cylindrical, it is to be understood that other shapes are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.